Steer drive wheel mechanism

This application claims the benefit of the Korean Patent Application No. 10-2023-0022746, filed on Feb. 20, 2023, which is hereby incorporated by reference as if fully set forth herein.

The current invention pertains to steer-drive wheel systems, specifically focusing on powered wheel mechanisms utilized in the development of drive systems for mobile platforms. These platforms include wheeled mobile robots, autonomous mobile robots (AMRs), automated guided vehicles (AGVs), motorized wheelchairs, forklifts, and various other wheeled mobility devices.

Various configurations of mobile platforms have been developed, typically featuring a base or platform, drive systems, controllers, sensors, manipulators, and necessary equipment for the platform's intended operations. These platforms can be driven by wheels, tracks, “legs,” or other means. Maneuverability is a crucial aspect of mobile platforms, allowing them to navigate obstacles and perform tasks effectively. Increased maneuverability is associated with the ability to generate more independent degrees of freedom. For a mobile platform moving on a ground plane, this translates to a maximum of three degrees of freedom-two translational and one rotational. Full control over these degrees of freedom results in an omnidirectional system, while instantaneous control over their acceleration defines a holonomic system.

To achieve omnidirectional mobility, one or more steer drive wheels can be employed, pivoting about a vertical steer axis and rotating around a horizontal drive axis. The vertical steer axis may or may not intersect with the horizontal drive axis. When they do not intersect, an offset distance creates a caster wheel, enabling the platform to accelerate in any direction and making it holonomic.

Prior art in steer drive wheel mechanisms often involves two motors-one for steering and another for driving the wheel. Three common configurations exist for the installation of these motors. In the first, both steering and driving motors are installed on the wheel bracket, requiring electrical power and signals to be transferred from the platform through a slip ring to steer the wheel freely. The second configuration has only the driving motor on the wheel bracket, with the steering motor on the platform, necessitating a slip ring for free steering. The third configuration places both motors on the platform, transmitting driving power to the wheel through various mechanical drive train configurations, eliminating the need for a slip ring, a primary advantage of this setup.

However, the prior art of installing both motors on the platform has drawbacks arising from the mechanical structure using a single power train to transfer driving power from the motor to the wheel. In this setup, the torque generated by the driving motor is transmitted not only to the wheel but also to the wheel bracket, causing unintended steering for the wheel. This phenomenon is inevitable if a single drive train is used to transfer driving power from the motor to the wheel, and the torque generated initially travels parallel to the steer axis before being redirected to align with the drive axis, perpendicular to the steer axis.

Therefore, in conventional systems, maintaining the desired azimuth (or orientation) of the wheel without applying an additional counteracting torque is not achievable. This inevitably leads to unintended torque being imposed on the wheel frame along the steer axis, presenting challenges that require resolution.

Overcoming the unintended torque to maintain the desired azimuth and delivering steering torque when a change of azimuth is required necessitates the use of a dedicated azimuth (or steering) control system. Consequently, to maintain or alter the wheel's azimuth conventional technologies expend a significant amount of energy compensating for the counteracting torque equal to that delivered vertically along the steer axis by the driving motor.

Components of the steering control system experience continuous exposure to internal time-varying mechanical stresses, accumulating throughout wheel operation. For instance, common steering system components like the ring and pinion gear are in constant contact without relative rotation, leading to accelerated wear and fatigue due to stress concentration. Although the resisting torque and internal stress can be distributed by incorporating multiple steering motors, conventional systems face challenges in enhancing the dynamic steering agility of the wheel. This limitation stems from the typically restricted power available for the dedicated steering control system.

The practical use of a high torque/low-speed motor to drive the wheel is not feasible, as a high torque driving motor would intensify the burden on the steering motor in the steering control system, resulting in increased energy waste and mechanical stress.

The invention provides a method to construct a steer-drive wheel mechanism, where two electric motors, fixedly installed relative to a mobile platform, collaboratively drive and steer the wheel through coaxially arranged axes. This cooperative operation ensures efficient power utilization and minimizes unnecessary mechanical stresses. The continuous collaboration of the two motors in driving and steering the wheel can be achieved by using a ‘motion synthesizer,’ which combines two rotational motions from the motors to appropriately produce motions for driving and steering the wheel.

In accordance with the present invention, when the two rotational motions applied to the steerable wheel bracket by the motors are equal in magnitude but opposite in direction along the steer axis, the wheel can undergo a driving motion (rolling) without steering. Conversely, when the two rotational motions are equal in magnitude and direction along the steer axis, the wheel can experience steering motion without driving. Simultaneous generation of driving and steering motion is possible by controlling the magnitude and direction of the two rotational motions.

Furthermore, the present invention allows the configuration of a steer-drive wheel mechanism with either one or two driving wheels. A two wheeled steer-drive mechanism can be achieved by feeding the rotational motion produced by the “motion synthesizer” into a differential gear mechanism. This not only enables the steer-drive wheel to handle a larger payload but also facilitates steering the wheel with approximately 50% less steering torque compared to a single wheeled steer-drive mechanism.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The detailed descriptions that follow are provided to facilitate a comprehensive understanding of the methods, devices and/or systems described herein. However, this is only an example, and the present invention is not limited thereto.

In describing the embodiments of the present invention, if it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or operator. Therefore, the definition should be made based on the contents throughout this specification. The terminology used in the detailed description is only for describing the embodiments of the present invention and should in no way be limiting. Unless expressly used otherwise, singular forms of expression include plural forms. In this description, expressions such as “comprising” or “comprising of” are intended to indicate certain characteristics, numbers, steps, operations, elements, some, or combinations thereof, and one or more other than those described. It should not be construed to exclude the existence or possibility of any other feature, number, step, operation, element, part, or combination thereof.

In one embodiment of the present disclosure, the reference numerals of the components to be described below are assigned random numbers or letters for convenience of description, and the corresponding reference numerals do not mean higher or lower concepts between the components.

1 FIG. 2 FIG. 1 2 14 1 14 2 23 24 illustrates a conceptual embodiment of the invention, where two stationary motorsandcollaborate to transmit power to the wheel-and-.shows the ‘motion synthesizer’ which two input motions to generate two output motions. This design features a coaxial configuration of two axes, propelling both the motion synthesizerand subsequently the differential.

20 16 16 20 16 1 2 16 1 2 16 The wheel bracketis rotatably mounted on the fixed frame, which is attached to a mobile platform. The fixed frameremains stationary relative to the mobile platform. The wheel bracketrotates relatively freely with the fixed frameby the first motorand the second motormounted on the wheel bracket. That is, the first motorand the second motorrigidly installed on the fixed frameto collaborate in driving and steering the wheel.

20 16 30 16 6 7 20 16 6 7 30 The wheel bracketis rotatably mounted on the fixed framesuch that it can be steered about steer axisrelative to the fixed frame. The inner input shaftand the outer input shaft (hollow shaft)of the concentric biaxial structure are fastened to the same rotation axis as the wheel bracketand rotate relative to the fixed frame. The inner input shaftand an outer input shaftconfigured coaxially along steer axisto transmit two rotational motions generated by the first and the second motors, respectively.

1 6 2 7 1 2 6 7 20 16 30 4 13 20 1 2 6 7 14 13 20 30 16 The steer drive wheel mechanism comprises a first gear unit configured to transfer rotational motion of the first motorto the inner input shaft, and a second gear unit configured to transfer rotational motion of the second motorto the outer input shaft. Wherein the first motorand the second motorare configured, based on the inner input shaftand the outer input shaftgenerating rotational motion in the same magnitude and direction to each other, to rotate the wheel bracketrelative to the fixed frameabout steer axiswithout causing rotational motion of the wheelabout wheel axisrelative to the wheel bracket. Wherein the first motorand the second motorare configured, based on the inner input shaftand the outer input shaftgenerating rotational motion in the same magnitude but opposite direction to each other, to rotate the wheelabout the wheel axisrelative to the wheel bracketwithout causing rotational motion of the wheel bracket about the steer axisrelative to the fixed frame.

20 20 16 30 22 1 1 4 5 6 9 2 23 5 6 30 2 18 55 7 9 1 55 7 30 The rotational movement of the wheel bracketmeans that the wheel bracketrotates relative to the fixed framearound the steering axisthrough the steering bearing-. In this arrangement, motorsequentially drives gear, gear, inner input shaft, and horizontal bevel gear-within the motion synthesizer. The gearand the inner input shaftrotate around the steering axis. Similarly, motorsequentially turns gear, gear, outer input shaft, and horizontal bevel gear-. The gearand the outer input shaftrotate around the steering axis. In all figures, crossed rectangles represent bearings facilitating relative rotation.

9 1 9 2 23 8 1 8 2 28 1 28 2 10 20 20 16 30 8 1 8 2 23 20 16 1 FIG. Rotational motions of horizontal bevel gears-and-are combined inside the motion synthesizerby the two vertical bevel gears-and-attached to horizontal output shaft-and-, respectively. This combination produces rotational motion of vertical output shaftrelative to the wheel bracketand rotational motion of the wheel bracketrelative to the fixed frame. Both rotational motions occur about steer axis. It is very crucial to note that although two vertical bevel gears-and-are illustrated in, the minimum number of vertical bevel gear required for the motion synthesizeris one but three or more vertical bevel gears may be used to facilitate rotational motion of the wheel bracketrelative to the fixed frame.

1 FIG. 23 20 28 1 28 2 8 1 8 2 28 1 28 2 9 2 6 8 1 8 2 9 2 6 30 6 9 1 7 8 1 8 2 9 1 7 7 8 1 8 2 9 2 9 1 28 1 28 2 Referring to, in the motion synthesizer, the wheel bracketincludes at least one horizontal output shaft-and-and at least one vertical bevel gear-and-provided at the end of the horizontal output shaft-and-. At the bottom, the first horizontal bevel gear-provided at the bottom of the inner input shaftmay be meshed with the vertical bevel gears-and-. The first horizontal bevel gear-coupled to the inner input shaftand configured to be rotated about the steer axisby the inner input shaft. Similarly, At the top, the second horizontal bevel gear-provided at the bottom of the outer input shaftmay be meshed with the vertical bevel gears-and-. The second horizontal bevel gear-coupled to the outer input shaftand configured to be rotated about the steer axis by the outer input shaft. At least one vertical bevel gear-and-is engaged with both the first horizontal bevel gears-and the second horizontal bevel gears-and coupled to the horizontal output shaft-and-.

23 6 7 14 20 20 16 10 6 28 1 28 2 23 6 7 28 1 28 2 That is, the motion synthesizeraccepts two rotational motions from the inner outer input shaftand the outer input shaftand produces rolling (or driving) motion of the wheelrelative the wheel bracketand steering motion of the wheel bracketrelative to the fixed frame. The vertical output shaftextended from inner input shaftand at least one horizontal output shaft-and-. The gear unit is disposed within the motion synthesizer, the gear unit coupled to the inner input shaft, the outer input shaft, at least one the horizontal output shaft-and-.

1 FIG. 1 2 r s 16 6 7 10 20 20 16 In, ωand ωdenote angular velocities, relative to the fixed frame, of the two coaxially arranged shafts: the inner input shaftand the outer input shaft, respectively. Additionally, ωand ωdenote the angular speed of the vertical output shaftrelative to the wheel bracketand steering angular speed of the wheel bracketrelative to the fixed frame, respectively.

r r r 1 2 14 1 14 2 20 79 80 The rolling (or driving) angular speed of the wheel Ωis defined by the average of the angular velocities of two wheels-and-relative to the wheel bracket. Ωis a constant multiple of ω, where the constant is determined by the gear ratio between bevel gearsand. The arrows associated with angular velocities indicate the direction of rotation according to the right-hand rule. Notice that the directions of ωand ωare defined as opposite to each other for convenience.

2 FIG. 23 8 1 8 2 28 1 28 2 9 1 9 2 28 1 28 2 shows exclusively the motion synthesizer, wherein vertical bevel gears-and-coupled to the horizontal output shaft-and-, respectively, engage with both horizontal bevel gears-and-. Denoting the angular speed of the horizontal output shafts-and-by

23 1 2 r the role of the motion synthesizercan be expressed in kinematic relationship involving ω, ω, ω,

s and ωas follows:

9 1 8 1 23 1 2 r s where a is a constant determined by the gear ratio between bevel gears-and-. Here ωand ωmay be considered as inputs to the motion synthesizer, while ω, ω, and

23 serve as outputs of the motion synthesizer. It is worth noting that

1 2 r s can also be used to drive wheel(s) as will be shown in alternative embodiments. The inverse kinematic relationship among ω, ω, ω, and ωcan also be obtained as

1 2 and the inverse kinematic relationship among ω, ω,

s and ωcan also be obtained as

1 2 s 1 2 r Equations (1-1), (1-2), and (1-3) imply that when ωand ωpossess equal magnitudes but opposite directions, as indicated by arrows, only wheel's rolling motion occurs because ωis equal to zero, i.e., no steering motion. And when ωand ωhave equal magnitudes and the same directions, only steering motion of the wheel takes place, as ωand

r s 1 2 are both zero, i.e., no rolling motion. These two operational conditions guarantee that the collaboration between two motors in driving and steering the wheel is really feasible through the present invention. Meanwhile, in a general scenario where both ωand ωneed to be nonzero to simultaneously drive and steer the wheel, the corresponding ωand ωcan be determined from Eqns. (2-1) and (2-2), and when both

s 1 2 and ωare required to be nonzero for simultaneous driving and steering, corresponding ωand ωcan be obtained from Eqns. (3-1) and (3-2).

14 1 14 2 30 13 20 14 1 14 2 13 20 14 1 14 2 14 1 14 22 13 20 22 4 In addition, at least one wheel-and-is rotatably mounted on the wheel bracketthrough a wheel axis. Specially, the wheel bracketincludes at least one wheel-and-fixed to at least one wheel axisthat can rotate relative to the wheel bracket. The rolling motion of the wheel-and-means the rotating motion of the wheel-and-fixed to the wheel axisrelative to the wheel bracketthrough the wheel axis bearing-.

1 FIG. 23 10 79 24 80 13 26 1 26 2 29 80 26 1 26 2 27 1 27 2 13 24 20 10 23 24 20 28 1 28 2 23 In, the rotational motion output from the motion synthesizerthrough the vertical output shaftdrives pinion bever gearfor differentialto rotate the ring geararound the wheel axis. At least one spider gear-and-is installed on the spider gear carrierfixed to the ring gear, and at least one spider gear-and-is engaged with the first bevel gear-and the second bevel gear-coupled to the left and right wheel axis. The differentialcan be attached to the wheel bracketto accept rotational motion of the vertical output shaftof the motion synthesizeras input and produce two output rotational motion for driving the wheel. In some cases, the differentialcan be attached to the wheel bracketsuch that it accepts rotational motion of one of the horizontal output shafts-and-of the motion synthesizeras input and produces two output rotational motion for driving the wheel.

24 20 10 23 14 1 14 2 24 26 1 26 2 26 1 26 2 13 80 29 26 1 26 2 29 14 1 14 2 1 FIG. The differentialis attached to the wheel bracket, accepts rotational motion of the vertical output shaftof the motion synthesizeras the input to produce two output rotational motions for driving the wheel-and-.shows an embodiment in which the differentialcomprises the first spider gear-and the second spider gear-. The spider gears-and-rotate around the wheel axistogether with the ring gearto which the spider gear carrieris fixed. At the same time, the spider gears-and-rotate relative to the spider gear carrierwhen the rotation speeds of the left wheel-and the right wheel-are different.

24 In addition, in the present invention, the differentialuses a bevel gear as a representative example, but it can be modified and used as a variety of differential gear devices that ramifies one rotational motion input into two independent rotational motion outputs. (ex. Method using spur gears, method using epicyclic gear structure, Torsen method, etc.)

3 FIG. presents a conceptual embodiment of current invention, demonstrating the transmission of the rotational motion from the vertical output shaft to the wheel.

3 FIG. 1 FIG. 32 31 10 13 14 31 32 10 23 13 shows an embodiment in which rotational motion is transmitted to the ring bevel gearthrough the pinion bevel gearinstalled on the vertical output shaftshown into generate rolling motion in the wheel shaftand wheel. This is achieved through internal gear meshing between the pinion bevel gearand ring bevel gear, resulting in the rotation of wheel rotation Q, about a skewed axis. That is, the steer drive wheel mechanism comprises a power train unit that transmits the rotational motion of the vertical output shaftof the motion synthesizerto a skewed wheel axis.

4 FIG. 10 13 34 illustrates comparable concept of generating wheel rotation about a skewed axis, wherein the rotational motion of vertical output shaftis conveyed to wheel shaftthrough either constant velocity joint or bevel gear meshing.

5 FIG. Moving on to, a conceptual embodiment of the current invention is showcased, utilizing the output rotational motion

28 1 23 14 13 11 1 11 2 11 3 28 1 13 of the horizontal output shaft-of motion synthesizerto induce the rotation of the wheelabout wheel axis. This is accomplished through a series of gear meshing among gears-,-, and-. It is essential to note that the transmission of power between output shaft-and wheel axiscan be achieved through various other means, such as a timing belt or bevel gear meshing. Additionally, the output rotational motion

28 2 28 1 23 28 1 23 13 of the horizontal output shaft-, instead of the horizontal output shaft-, of motion synthesizercan serve the same purpose. That is, the steer drive wheel mechanism comprises a power train that transmit the rotational motion of the horizontal output shaft-of the motion synthesizerto the wheel axis.

6 FIG. 43 13 24 43 41 13 24 42 20 14 depicts a conceptual embodiment of the current invention, introducing an offset distancebetween the wheel axisand the output axis of the differential. This offset allows the platform to achieve acceleration in any direction on the ground plane. Specially, the offset distancecan be set by using a method in which the gearinstalled on the wheel axisof the differentialengages the gearinstalled on the wheel bracketto drive the wheel.

7 FIG. In, a conceptual embodiment of the current invention is shown, where the output rotational motion

28 1 23 24 43 of the horizontal output shaft-of motion synthesizeris directly fed into the differential. This configuration naturally results in the introduction of an offset distance.

8 FIG. 1 2 6 7 23 illustrates a conceptual embodiment of the current invention, showcasing the arrangement of two stacked motorsand. This motor configuration, where the motor shafts are directly linked to the input shaftsandof the motion synthesizer, proves particularly practical when high torque motors are feasible. This same motor arrangement can be implemented in any of the conceptual embodiments presented thus far.

9 FIG. 5 FIG. As an illustration,demonstrates the outcome of altering the motor configuration depicted in.

10 FIG. 1 50 1 50 1 51 6 2 52 2 50 2 53 7 In, an alternative motor installation variation is depicted, where two horizontally arranged motors deliver power to the motion synthesizer through bevel gear meshing. The motor shaft of the first motoris positioned horizontally and connected to the pinion bevel gearfor the first motor. The pinion bevel gearfor the first motoris engaged with the ring gearattached to solid inner input shaft. Similarly, the motor shaft of the second motoris positioned horizontally and connected to the pinion bevel gearfor the second motor. The pinion bevel gearfor the second motoris engaged with the ring gearattached to solid outer input shaft.

11 FIG. 11 FIG. 1 2 16 21 Moving to, a conceptual embodiment of the current invention reveals a configuration where two motors are positioned beneath the motor housing.shows the motorsandof the present invention are mounted beneath the fixed frameto facilitate easy installation of the active caster wheel underneath the mobile platform.

23 It is essential to note that various potential variations in the arrangement of two motors exist, although not all are detailed in this document. For instance, two horizontally arranged motors could be configured to transfer power to the motion synthesizerthrough worm gear and worm wheel meshing, providing a substantial gear ratio within limited space. Additionally, the option of replacing two motors with two groups of motors is also feasible

12 FIG. 24 In, a conceptual representation of the current invention is presented, featuring a differentialconfiguration using spur or helical gears instead of bevel gears. Alternative differentials, such as Torsen differential or epicyclic differential, can also be employed.

13 FIG. 13 FIG. 28 1 28 2 14 28 1 28 2 14 11 1 11 3 12 1 12 4 11 1 11 3 12 1 12 4 11 2 11 1 11 3 12 2 12 3 12 1 12 4 shows a conceptual embodiment of the current invention, where the two rotational motions derived from both horizontal output shafts-and-of the motion synthesizer are used to propel the wheel. It is noteworthy that angular speed of the horizontal output shafts-and-are equal in magnitude but opposite in direction. To ensure that both rotational motions of the two horizontal output shafts contribute in a synergetic way to the rotation of the wheel, two constraints must be imposed on the design of power train: Firstly, the gear ratio between gears-and-must be equal to the gear ratio between gears-and-. Secondly, the gear train between gears-and-must be configured differently from the gear train between gears-and-such that both gear trains create an identical angular speed of the wheel, both in magnitude and in direction.illustrates, among many possibilities, one potential configuration of these gear trains, wherein only one gear-is inserted between gears-and-, while two gears-and-are inserted between gears-and-. Note that timing belt or chain can be used instead of gears.

23 9 2 9 1 8 1 8 2 In this case, the gear unit of the motion synthesizercomprises the first horizontal bevel gear-, the second horizontal bevel gear-, the first vertical bevel gear-, the second vertical bevel gear-, a first drive train unit, and a second drive train unit.

8 1 9 2 9 1 28 1 8 2 9 2 9 1 28 2 The first vertical bevel gear-is engaged with both the first horizontal bevel gear-and the second horizontal bevel gear-and coupled to a first horizontal output shaft-. The second vertical bevel gear-is engaged with both the first horizontal bevel gear-and the second horizontal bevel gear-and coupled to a second horizontal output shaft-.

8 1 13 11 1 11 3 11 2 8 2 13 12 1 12 4 12 2 12 2 The first drive train unit transmits the rotational motion of the first vertical bevel gear-to the wheel axis. The first drive train unit comprises gears-and-. The first drive train unit can comprise additionally gear-. The second drive train unit transmits the rotational motion of the second vertical bevel gear-to the wheel axis. The second drive train unit comprises gears-and-. The second drive train unit can comprise gear-and-additionally. The difference between the number of gears constituting the first drive train unit and the number of gears constituting the second drive train unit is an odd number. Wherein the first and the second drive trains are configured to deliver the same rotational motion both in magnitude and direction to the wheel axis when the first vertical bevel gear and the second vertical bevel gear rotate with same angular speed but in opposite direction relative to the wheel bracket.

14 FIG. 13 FIG. 13 FIG. 14 FIG. 13 FIG. 23 8 1 9 2 8 2 9 1 13 6 7 13 Whileillustrates a minor alteration to the motion synthesizer shown in, the result brings about a significant shift in the operation of gear trains. The fundamental difference in this configuration of the motion synthesizer arises from how bevel gears are engaged inside the motion synthesizer. In this setup, the vertical bevel gear-engages only with horizontal bevel gear-, while vertical bevel gear-engages only with the horizontal bevel gear-. This arrangement establishes two distinct drive trains, both converging at the wheel axis, where they mutually interact. Consequently, unlike the configuration depicted in, there is no theoretical constraint on the arrangement of two drive trains between the inner and the outer shafts,and the wheel shaft, allowing for the design of two independent drive trains with complete freedom., however, discloses one of myriad examples of configuring these two drive trains, ensuring they satisfy the same constraints as the configuration shown in. This specific configuration is practical, assuming the use of two identical motors to maintain symmetric collaboration. It is crucial to note that Eqns. (1-2), (1-3), (3-1), and (3-2) remain valid for this configuration.

23 9 2 9 1 8 1 8 2 In this case, the gear unit of the motion synthesizercomprises the first horizontal bevel gear-, the second horizontal bevel gear-, the first vertical bevel gear-, the second vertical bevel gear-, a first drive train unit, and a second drive train unit.

8 1 9 2 28 1 8 2 9 1 28 2 The first vertical bevel gear-is engaged with the first horizontal bevel gear-and coupled to a first horizontal output shaft-. The second vertical bevel gear-engaged with the second horizontal bevel gear-and coupled to a second horizontal output shaft-.

8 1 13 11 1 11 3 11 2 8 2 13 12 1 12 4 12 2 12 2 The first drive train unit transmits the rotational motion of the first vertical bevel gear-to the wheel axis. The first drive train unit comprises gears-and-. The first drive train unit can comprise gear-more. The second drive train unit transmits the rotational motion of the second vertical bevel gear-to the wheel axis. The second drive train unit comprises gears-and-. The second drive train unit can comprise gear-and-more. The difference between the number of gears constituting the first drive train unit and the number of gears constituting the second drive train unit is an odd number

15 FIG. 14 FIG. 61 62 23 61 65 63 64 13 61 62 Maintaining the same idea of symmetric collaboration of two identical motors,shows a noteworthy alteration of the idea displayed in, In this instance, spur or helical gears,replace bevel gears within the motion synthesizerand rotational motion of gearis directly transmitted, through vertical shaft, to the bevel pinion gearmeshing with the bevel gearcoupled to the wheel axis, leading to a substantial simplification of the drive train. Equations (1-2), (1-3), (3-1), and (3-2) remain also valid for this configuration with a constant a determined by the gear ratio between gearsand.

21 16 20 14 1 2 6 7 23 A steer drive wheel mechanism for a mobile platformcomprises a fixed frame, wheel bracket, at least one wheel, a first motorand a second motor, an inner input shaftand an outer input shaft, and a motion synthesizer, and a gear unit.

16 16 20 16 30 16 14 20 13 1 2 16 14 6 7 30 1 2 Similarly, the fixed frameremains stationary relative to the mobile platform. The wheel bracketis rotatably mounted on the fixed framesuch that it can be steered about steer axisrelative to the fixed frame. At least one wheelis rotatably mounted on the wheel bracketthrough a wheel axis. The first motorand the second motorare rigidly installed on the fixed frameto collaborate in driving and steering the wheel. The inner input shaftand the outer input shaftare configured coaxially along steer axisto transmit two rotational motions generated by the first motorand the second motor.

23 6 7 65 1 65 2 23 6 7 65 1 65 2 However, in this case, the motion synthesizercan accept two rotational motions from the inner input shaftand the outer input shaftand produce two rotational motions of a first vertical shafts-and a second vertical shafts-. The gear unit can be disposed within the motion synthesizer, the gear unit coupled to the inner input shaft, the outer input shaft, the first vertical shaft-, and the second vertical shaft-.

62 1 62 2 61 1 61 2 62 1 6 30 6 62 2 7 30 7 61 1 65 1 62 1 61 2 65 2 62 2 Moreover, the gear unit can comprise a first horizontal gear-, a second horizontal gear-, a third horizontal gear-, a fourth horizontal gear-. The first horizontal gear-is coupled to the inner input shaftand configured to be rotated about the steer axisby the inner input shaft. The second horizontal gear-is coupled to the outer input shaftand configured to be rotated about the steer axisby the outer shaft. The third horizontal gear-is coupled to the first vertical shaft-and engaged with the first horizontal gear-. The fourth horizontal gear-is coupled to the second vertical shaft-and engaged with the second horizontal gear-.

65 1 13 65 2 13 63 1 64 1 63 2 64 2 20 The steer drive wheel mechanism further comprises a first gearset to transmit the rotational motion of the first vertical shaft-to the horizontal wheel axis, and a second gearset unit to transmit the rotational motion of the second vertical shaft-to the horizontal wheel axis. The first gear set comprises pinion gear-and ring gear-and the second gear set comprises pinion gear-and ring gear-. Both gear sets are configured to rotate relative to the wheel bracket.

1 6 2 7 16 The steer drive wheel mechanism further comprises a first gearset configured to transfer rotational motion of the first motorto the inner input shaft, and a second gearset configured to transfer rotational motion of the second motorto the outer input shaft. Both gear sets are configured to rotate relative to the fixed frame.

The preceding descriptions and illustrations are provided solely for demonstrative purposes and do not encompass all potential alternative embodiments of the invention. It is important to recognize that the present invention is not restricted to the specific embodiments described above and depicted herein, but rather includes all variations that fall within the scope of the appended claims.